As set forth in the above related applications and as otherwise well known, a hand-manipulatable trackball, touch tablet, mouse, or joystick has been used with a computer keyboard for moving a cursor on a CRT display. Likewise, it is known to have a control mechanism, including a rotatable shaft and a freely slidable sleeve member on the shaft to separately move linearly with respect to the shaft and move rotatively with the shaft. First and second analog valves, representing X and Y axis coordinates, for example, can be adjusted in mechanically actuated transducers such as potentiometers or other encoders by rotation of the shaft and linear movement of the member, respectively. Such mechanisms have been placed proximate to the keyboard so that a user's hand can be moved to effectuate the above movements and signal generation. Mechanisms of this type have also been constructed so that slight downward pressure on the shaft or sleeve member will actuate an electrical switch for enabling a circuit in the apparatus being controlled.
While the control mechanism described above is suitable for a number of applications, such a mechanism can be simplified so that a control mechanism can be constructed with fewer moving parts yet the simplified control mechanism can provide precision control of a pair of analog values, such as the X-Y position of the cursor of a computer display. The present invention provides such a simplified mechanism.
In the preferred construction of the related first application, the shaft on which the cylinder travels must have a precision shaft surface which is exposed to permit full travel of the cylinder, thus exposing the working mechanism and bearings to contamination. Further, the shaft bearing surface is also used as an operator contact surface with conflicting requirements for surface texture in the latter and smooth bushing surface in the former, along with generally nonoptimized ergonomics and appearance. The position of the cylinder on the shaft, in use, is constantly changing, depriving the user of a fixed reference and causing disorientation, i.e. the user can lower his thumb to the point where he thought the cylinder was residing but finds it is no longer there. Also in the prior devices, in pure horizontal movement, one side of the finger rests against the cylinder and the other rests and drags across a fixed edge of the housing to provide a ruler-like steady fixed reference. This friction degrades operation and contributes to a noticeable amount of vertical drift in the horizontal movement.
The prior art devices now in use (trackballs, mice, joysticks, etc.) have not been ergonomically designed to permit optimum positioning within a control panel or keyboard nor have they been designed for efficient thumb operation, the thumb being a digit of the hand with great dexterity. Because of their size or the nature of their operation, these devices do not lend themselves to symmetrical centering between the home hand positions for ambidextrous accessibility.